In the course of dyeing materials, particularly plastics, it is sometimes desirable to color very large and heavy articles such as coated glass sheets, plastic sheets, furniture, large volume water bottles and automobile windows. Some of these articles may be large, e.g., up to 5 feet wide by 10 feet long, and weigh in excess of 300 pounds. In these instances, it is more economical and environmentally attractive to color large articles using spray processes because spray processes significantly reduce the required volume of coloring solution and eliminate the need for large volume dipping tanks. Hence vessels containing the dye solutions, as well as ancillary equipment such as pumps and heaters, can be smaller, and consequently, less expensive. Also, the smaller quantities of dye-containing solution discarded as the result of a color change can be reclaimed more efficiently.
In addition to using less solution, spray processes also allow large articles to be easily transported via a simple conveyer into an enclosed spray apparatus where both coloring and subsequent rinsing take place. Once coloring and rinsing are completed, the articles are simply conveyed out of the spray apparatus for drying and packaging. In contrast, if similarly sized articles are immersed in coloring solutions, expensive cranes, requiring buildings with high bay areas, must be used to convey and lift heavy articles into and out of huge vats of hot solution. Moreover, these vats open to the atmosphere and create a potential for introducing vapors into the environment. Also, there is a problem with solution cross-contamination as the articles are lifted from one vat to another, dripping solution as they move. Another objection to the immersion technique is that due to their size, the articles cannot be moved in and out of the vats quickly enough to avoid non-uniformity in the color.
U.S. Pat. No. 6,994,735 describes a method of spraying dye solutions onto plastic articles to add color to the article. However, no apparatus for performing such operations is described.
It would be desirable to have an efficient apparatus for spraying dye-containing solutions and associated rinse solutions onto relatively large substrates.